<!DOCTYPE html>
<html>
<head lang="en">
    <meta charset="UTF-8">
    <title></title>
</head>
<body>
    <button id="btn">btn</button>
    <script>
        function DOMWrapper(element){
            this.element = element;
        }
        DOMWrapper.prototype.addClass = function(className){
            this.element.className += " " +className;
        };
        DOMWrapper.prototype.remove = function(){
            this.element.parentNode.removeChild(this.element);
        };
        var wrapper = new DOMWrapper(document.getElementById("btn"));
        wrapper.addClass("bb");
        wrapper.addClass("ab");

        var e = document.getElementById("btn");
        e.className +=" "+"cc";
    </script>
</body>
</html>